Immigrants come to the U.S. determined to make a new life. So often they're more open to the kind of changes we'll need to deal with climate change.

For environmentalists, population has long been a problem. Many of the things we do wouldn't cause so much trouble if there weren't so many of us. It's why I wrote a book some years ago called "Maybe One: An Argument for Smaller Families." Heck, it's why I had only one child.

And many of us, I think, long viewed immigration through the lens of population; it was another part of the math problem. I've always thought we could afford historical levels of immigration, but I understood why some other environmentalists wanted tougher restrictions. More Americans would mean more people making use of the same piece of land, a piece that was already pretty hard-used.

In recent years, though, the math problem has come to look very different to me. It's one reason I feel it's urgent that we get real immigration reform, allowing millions to step out of the shadows and on to a broad path toward citizenship. It will help, not hurt, our environmental efforts, and potentially in deep and powerful ways.

One thing that's changed is the nature of the ecological problem. Now that global warming is arguably the greatest danger we face, it matters a lot less where people live. Carbon dioxide mixes easily in the atmosphere. It makes no difference whether it comes from Puerto Vallarta or Portland.

It's true that the typical person from a developing nation would produce more carbon once she adopted an American lifestyle, but she also probably would have fewer children. A December report from the Pew Research Center report showed that birthrates in the U.S. were dropping faster among Mexican American women and women who immigrated from Mexico than among any other group.

This is a trend reflected among all Latinas in the U.S. As an immigrant mother of two from the Dominican Republic told the New York Times: "Before, I probably would have been pressured to have more, [but] living in the United States, I don't have family members close by to help me, and it takes a village to raise a child. So the feeling is, keep what you have right now." Her two grandmothers had had a total of 27 children. The carbon math, in other words, may well be a wash.

But there's a higher math here that matters much more. At this point, there's no chance we're going to deal with global warming one household at a time — scientists, policy wonks and economists have concluded it will also require structural change. We may need, for example, things such as a serious tax on carbon; that will require mustering political will to stand up to the fossil fuel industry.

And that's precisely where white America has fallen short. Election after election, native-born and long-standing citizens pull the lever for climate deniers, for people who want to shut down the Environmental Protection Agency, for the politicians who take huge quantities of cash from the Koch brothers and other oil barons. By contrast, a 2012 report by the Sierra Club and the National Council of La Raza found that Latinos were eager for environmental progress. Seventy-seven percent of Latino voters think climate change is already happening, compared with just 52% of the general population; 92% of Latinos think we have "a moral responsibility to take care of God's creation here on Earth."

These numbers reflect, in part, the reality of life for those closer to the bottom of our economy. Latinos are 30% more likely to end up in the hospital for asthma, in part because they often live closer to sources of pollution.

But immigrants, by definition, are full of hope. They've come to a new place determined to make a new life, risking much for opportunity. They're confident that new kinds of prosperity are possible. The future beckons them, and so changes of the kind we'll need to deal with climate change are easier to conceive.

Republicans think immigrants are a natural fit for their party, and I hope they're at least partly right — some force needs to help ease the Republicans out of their love affair with ideology and back into a relationship with reality. As commentator Bill O'Reilly put it as he watched Mitt Romney lose despite gaining a huge majority of white votes, "it's not a traditional America anymore."

He's right. And for the environment, that's good news. We need immigrants to this nation engaged in public life, as soon and as fully as possible. It's not just the moral thing to do, it's a key to our future.

Bill McKibben is the founder of 350.org and a professor at Middlebury College.